On the validity of the quasiresonant approximation for molecular infrared-multiphoton excitation

Abstract

Quantum dynamical calculations of the IR-multiphoton excitation of two molecular model systems are presented. One is an anharmonic oscillator and the other the rovibrational structure of the lowest three excitation steps in the stretching manifolds of the ozone molecule. Systematic comparisons are made between solutions using either the Floquet approximation or the weak field quasiresonant approximation (WF-QRA). The WF-QRA is shown to be adequate for typical transition moments in molecular many level systems and intensities up to the TW cm−2 range in agreement with previous analytical considerations. The implications of these findings for an efficient approach to the computational treatment of IR-multiphoton excitation and for the mechanism of molecular IR-multiphoton excitation as a series of stepwise one photon transitions are discussed.